In recent years, in-vehicle silencing is being dramatically promoted from viewpoints of both a car body structure and control. This causes a situation such that an engine sound cannot appropriately bring the realism of running.
Therefore, a sound effect (also referred to as an active engine sound) generation apparatus is proposed. The sound effect generation apparatus detects driver's driving amount and generates, in a vehicle, a sound effect of an engine according to the driving amount through an in-vehicle speaker.
A sound effect generation apparatus disclosed in Patent Literature 1 includes fundamental frequency setting means for setting a fundamental frequency related to the number of cylinders and a rotation speed of an engine, harmonic determining means for determining a plurality of harmonics of the fundamental frequency, and gain determining means for determining a harmonic-enhanced gain of the engine. The gain determining means includes a circuit that determines an engine load. The engine load determination circuit includes at least one of an accelerator pedal position determination circuit, a mass airflow determination circuit, a negative pressure determination circuit, and an engine torque determination circuit. The engine load determination circuit adjusts a harmonic enhancing level based on the harmonic-enhanced gain.
This configuration causes vehicle occupants including a driver to feel a startlingly realistic engine sound.
Further, a vehicle control device disclosed in Patent Literature 2 includes operation amount detecting means for detecting an operation amount of operation means to be operated during acceleration, transient operation amount arithmetic means for calculating a transient operation amount based on a stationary state of the operation means, speed arithmetic means for calculating an operating speed of the operation means, and target arithmetic means for calculating at least one of a target acceleration and a target sound pressure that increase by an increase exceeding a differential threshold per time when a human can perceive stimuli received. At least one of a torque generation device and an in-vehicle acoustic device is controlled based on at least one of the target acceleration and the target sound pressure.
This configuration offers comfortable acceleration performance and acceleration feeling to a driver.
Normally, a sound recognized by a person is an auditory phenomenon caused by a fluctuation (a sound wave) of an air pressure, and its property is roughly classified into three parts including a volume, a tone, and a timbre.
Herein, the volume is related to a sound pressure level, the tone is related to a frequency, and the timbre is related to a sound quality.
When a fundamental wave sound having a fundamental frequency component and an integer-order component wave sound having an integer-order (secondary or more) frequency component with respect to the fundamental wave sound are simultaneously generated, a concord in which both the sounds are mixed together is formed without a beat (interference) between the sounds because an integer-order adjustment wave sound (a component wave sound) of the integer-order frequency component is an overtone series of the fundamental wave sound.
On the contrary, when the fundamental wave sound and a component wave sound having a frequency component other than the integer-order (secondary or more) frequency component with respect to the fundamental wave sound are simultaneously generated, a discord (an unclear sound) is generated by the interference between the sounds because an adjustment wave sound to be synthesized with the fundamental wave sound is not an overtone series of the fundamental wave sound.
In the sound effect generation apparatus in Patent Literature 1, realism of an engine sound during actual running of a vehicle and characteristics of engine sounds that vary with vehicle types are artificially reproduced by setting a gain for enhancement per frequency component wave sound.
Further, in the vehicle control device in Patent Literature 2, a sound effect according to an increase in acceleration of a vehicle is generated by setting a target sound pressure level of a high-frequency component wave sound of an engine sound.
However, in the sound effect generation apparatuses in Patent Literature 1 and 2, since a harmonic-enhanced gain and a target sound pressure level are determined by using only an operation amount of an accelerator pedal as a parameter, when a vehicle behavior and a sound effect do not match with each other, the sound effect is not congruent with a driver's will and thus the driver might have a feeling of strangeness.
For example, when a vehicle moves on a road surface such as a frozen road surface with a low road surface friction coefficient μ, even if a driver performs a steering operation, a turning operation is inhibited, and thus an actual turning amount of the vehicle is less than a steering amount. Further, when the vehicle runs on an ascending road having predetermined gradient, even if the driver performs a steering operation, a turning operation is inhibited, and an actual turning amount of the vehicle is less than a steering amount.
That is, in the above condition (the inhibition condition) such that the correspondence between an amount of an operation performed by the driver and an actual vehicle behavior is inhibited, when the sound effect generation apparatus generates a sound effect corresponding to the amount of the operation by the driver although actual operability of the vehicle is degraded, the driver have a feeling of strangeness for the sound effect due to mismatch between the vehicle behavior and the sound effect.